Fold your round tablecloth like this. I think I folded it 4 times, but it doesn't matter, just make sure the ends are even and it comes to a point.
Use something round to trace a portion of a circle on the point. The round object you use should be the size you want your center opening to be. Make sure your point is at the center of the circle when you trace. Cut it out.
Now use one of the fold lines to cut a straight line from the edge of the table cloth to the center.
Hem both of these new raw edges and the inside circle by folding it over twice and sewing down.
This is optional but I chose to add some velcro so the opening would stay closed. If you decide to do the same, attach one strip to the inside of the opening and one strip to the outside as shown above.
Last step is to add some fun trim! I took my tablecloth to the fabric store with me to make sure I got enough. Didn't it come out cute? So easy.